1. Technical Field
The present invention relates to a thin-film device, a method for manufacturing the thin-film device, and a display. In particular, the display is manufactured in such a manner that an active matrix driving circuit including thin-film devices is separated from a substrate, which is the original, and then transferred to a second substrate.
2. Related Art
Conventional thin-film devices for displays are formed on rigid substrates such as glass substrates. If such thin-film devices are formed on lightweight plastic substrates, advantages such as weight reduction, thickness reduction, and shatter prevention can be achieved.
JP-A-10-125931 (hereinafter referred to as Patent Document 1) discloses a technique for transferring thin-film devices fabricated on a first substrate, which is the original, to a second substrate in one step. If the technique is used to manufacture a display, pixel electrodes and external connection terminals need to extend to a peel-off surface.
Patent Document 1 provides a structure in which pixel electrodes 1700 extend through an interlayer insulating layer to a separation layer 3100 and an electrode made of indium tin oxide (ITO) or aluminum extends to a peel-off surface. In such a structure, circuit components such as transistors and storage capacitors cannot be arranged in a region containing the pixel electrodes 1700.
Active matrix-type electrophoretic and liquid crystal displays include pixel circuits, which usually include selection transistors for selecting pixels and storage capacitors for holding the potential of pixel electrodes. In particular, the storage capacitors preferably have high capacity because components of the electrophoretic displays have a long response time of, for example, several hundred milliseconds. In the electrophoretic and liquid crystal displays, no circuit components can be arranged in regions containing the pixel electrodes; hence, it is difficult to allow the storage capacitors to have high capacity. In order to allow the storage capacitors to have high capacity, the pixel electrodes need to have a small size. This leads to a reduction in aperture ratio. Therefore, there is a problem in that the electrophoretic and liquid crystal displays suffer from low contrast. Furthermore, there is a problem in that an increase in definition leads to a reduction in aperture ratio at the same storage capacitance. The term “aperture ratio” used herein means the percentage of a pixel electrode in one pixel, that is, the area percentage of a pixel electrode, serving for display, in each pixel.
In order to solve the above problems, the following technique has been proposed as disclosed in JP-A-2001-125138 (hereinafter referred to as Patent Document 2): a technique for forming the same structure as that present on a first substrate, which is the original, on a third substrate through two transfer steps. According to this technique, the same surface structure as that of the first substrate is obtained on the third substrate and therefore driving circuits can be formed on a plastic substrate by the same process as that for fabricating ordinary thin-film transistors. That is, unlike a process for transferring a thin-film device in one step, pixel electrodes need not extend to a peel-off surface; hence, circuit components can be fabricated in a region containing the pixel electrodes so as to be located at a level different from a level at which the pixel electrodes are arranged. This provides sufficient storage capacitance without causing a reduction in aperture ratio.
However, this technique includes the two transfer steps and therefore is complicated. This technique has problems such as high cost and low yield. Therefore, the following process has been demanded: a low-cost process for manufacturing a thin-film device, having substantially the same circuit function as that of a thin-film device manufactured through two transfer steps, in one transfer step.